System for line monitoring in an energy chain

ABSTRACT

A system for monitoring the state of a cable, which is guided in an energy chain between a base and a movable driver element. The movable energy chain forms a movable run at a driver element, a resting run at a base and, between the two runs, a deflecting bend. A monitoring device having at least one indicating element at the energy chain evaluates an indicating-element signal and monitors whether an error state occurs. The indicating element has two electrical indicating conductors guided by the energy chain, which indicating conductors extend along the movable run, and the monitoring device comprises a measuring circuit for resistance measurement or conductance measurement. One end point of each indicating conductor is connected to the measuring circuit and the other end points of the indicating conductors are short circuited such that the indicating conductors form a measurement loop.

FIELD

The invention relates in general to a system for position and/or line monitoring in an energy guide chain. The invention relates specifically to a monitoring system for an energy guide chain which serves in dynamic guidance of at least one line, such as for example a cable, hose or the like, between a base and a moving end movable relative thereto. A system of the type in question on the one hand comprises an energy guide chain which is displaceable along a travel path and, in so doing, forms in variable manner, depending on moving end position, a mobile run with a connection end for the moving end, a stationary run with a connection end for the base and a deflection arc. On the other hand, the system comprises a monitoring device with at least one sensor unit arranged on the energy chain, wherein the monitoring device evaluates a signal generated using the sensor unit in order to monitor the occurrence of a fault condition during operation of the energy guide chain.

BACKGROUND

Various systems of this type are already known. For example, patent applications WO 2004/090375 A1 and WO 2013/156607 A1 disclose systems with a force sensor between the moving end and the energy guide chain, in order to monitor whether the forces arising lie within a tolerance range.

Patent application WO 2015/118143 A1 discloses a system with a mechanically acting sensor unit, which detects damage to the energy guide chain using a triggering cord. A similar system is known from JP 2009 052 714 A, wherein a break detection system with an optical fiber is proposed, i.e. a break can be detected on the basis of the quantity of light.

The above-stated systems have the drawback of in principle only detecting damage that has already occurred. They therefore in particular do not allow proactive or predictive maintenance.

A monitoring system capable of allowing condition-oriented maintenance was described in patent application EP 1 521 015 A2. Here, the degree of wear of the energy guide chain, for example wear-related abrasion on the narrow face of a chain link, is determined in locally defined manner for example using electromechanically acting wear elements. However, this system does not provide any information about the current position of the energy guide chain or about the condition of a guided line.

It is also already known to determine the expected service life of cables in energy guide chains using laboratory tests, on the basis of a characteristic increase in conductor resistance, which typically occurs only after many hundreds of thousands or millions of test cycles.

Finally, a monitoring system is already known in this connection from U.S. Pat. No. 7,023,217 B1 which allows detection of the wear condition of electrical conductors, in particular of ribbon cables, for example in a trailing cable installation. Here, a plurality of conductors of the ribbon cable are tested on the basis of complex circuitry with a relay multiplexer and a precision voltmeter. As a result of the complex circuitry and the proposed connection technology at the two connection ends of the energy guide chain, this solution is however not very suitable for use in practical or active operation of an energy guide chain.

SUMMARY

A first object of the present invention therefore consists in proposing a monitoring system suitable for ongoing operation which allows early identification of wear, in particular prior to a line break. The monitoring system is intended in particular to allow proactive or predictive maintenance to reduce or completely avoid downtime. It is intended to have the simplest possible construction and not to impair operation to any appreciable extent.

According to a first aspect, a monitoring system for condition monitoring of a cable in an energy guide chain is proposed.

To achieve the above-stated object, it is proposed, according to the invention, in a system that the sensor unit includes two electrical indicator conductors guided by the energy guide chain, which indicator conductors extend along the greater part of the length of the mobile run or for example along the entire length, and that the monitoring device comprise a circuit with a measurement device for measuring resistance or conductance. The first aspect further provides that in each case a proximal end point of each of the two indicator conductors, i.e. the end points at one of the two connection ends of the energy guide chain, are connected to the measurement device and the respective other or distal end points of the two indicator conductors are short-circuited. These end points of the two indicator conductors may end at a specific lengthwise position of the energy guide chain or preferably at the other distal connection end of the energy guide chain. As a result of the short circuit, the conductors form a measurement loop, the resistance or conductance of which is measurable by the measurement device. One feasible example is a continuous measurement loop which is not interrupted by a separate short-circuit component, i.e. the one indicator conductor represents the outward distance or the proximal-to-distal distance and the other indicator conductor represents the return distance or vice versa. A separate short-circuit component is more practical, however, since it allows the use of existing multicore cables and does not require a continuous measurement loop.

The core concept is so-to-speak that the circuit comprises a measurement device for measuring a resistance or conductance of the indicator conductor and that the indicator conductor takes the form of a loop, such that measurement may be performed single-endedly at the same connection end of the energy guide chain. In addition, the outward and return course increases the measured resistance value and approximately doubles the wear-related effect, which simplifies reliable early identification prior to core or strand breakage.

In a preferred further development of the first aspect, provision is made for the monitoring device to comprise an evaluation unit which includes an integrated logic circuit and a reference value memory.

The logic circuit may in this case receive an output signal from the measurement device and use it for comparison with at least one prestored reference value from the reference value memory.

The evaluation unit in this respect allows application-specific modular adaptation of the monitoring device, even in the case of an unchanging detection circuit topology, for example by suitable programming of the evaluation functions and/or variable storage of the operating parameters in the evaluation unit. The evaluation unit in this respect also allows, inter alia, a system of modular construction with a plurality of circuit modules, which, depending on the desired monitoring aspect, are in each case of like construction and independent of the indicator conductor used, for example one circuit type for position monitoring and one circuit type for line monitoring. In addition, flexible consideration of various variables, such as application- and operating time-dependent parameters and environmental parameters, for example energy guide chain length, radius of curvature, cycle number, temperature etc. is simplified. The detection circuit and the evaluation unit may be integrated as modules in a common assembly, optionally also on a printed circuit board, or constructed spatially separately.

In particular, to carry out a true measurement or instrumental detection of the electrical quantity, it is advantageous for the circuit to comprise a measurement device connected on the input side to the indicator conductor so as to detect the electrical quantity, in particular an electrical parameter of the indicator conductor, by quantitative measurement and on the output side to provide a signal for the evaluation unit which is dependent thereon. The term measurement may here be understood in the sense of the definition in DIN standard DIN 1319.

In particular, however, it is not only in the case of instrumental detection that the evaluation unit may include an integrated logic circuit, such as for example a microcontroller or the like, with a reference value memory for evaluating the detected or measured quantities in relation to one or more reference values, for example a tolerance range. The measurement device may be of any desired embodiment, optionally wholly analogue, part analogue and part digital or purely digital. Due to the preferably programmable logic circuit, the evaluation unit may be modular and optionally adapted to the measurement circuit. The reference value memory may also be separate from the actual evaluation unit, for example if the latter interrogates the former as required, but is preferably part of the logic circuit.

The modular construction for example allows application-adapted resistance or impedance measurement, independently of the indicator conductor used. Since the absolute value depends inter alia on the total length of the indicator conductor, which is intended to extend at least along the greater part of the length of the mobile run, the expected measured values are heavily dependent on the application in which the energy guide chain is being used. Through ongoing resistance or impedance measurement, for example, impending failure of wires due to fatigue fracture in an electrical cable may be relatively reliably predicted, as demonstrated further below in relation to the first aspect. Unlike the proposal for example in U.S. Pat. No. 7,023,217 B1, it is however unnecessary with the proposed evaluation unit to provide a redundant inactive energy guide chain or line solely for reference purposes.

The at least one indicator conductor extends preferably at least over the greater part of the length of the energy guide chain, in particular over the entire part of the length of the energy guide chain which is displaceable during operation. The indicator conductor in this case 5 preferably extends at least over the half of the length of the energy guide chain located close to the moving end or adjacent thereto, since this is where wear is generally greatest as a result of stress caused by tensile and shearing forces and atypical behavior most frequently occurs there. The indicator conductor is in this case intended to extend at least over the critical portion of the length of the energy guide chain, typically the first third viewed from the moving end.

The electrical indicator conductor may be embodied separately, as an additional line, or preferably as a component part of a cable used in the application. The indicator conductor is in both cases preferably guided in the same way as an active line and in the energy guide chain, in particular right from one end of the energy guide chain to the other and optionally also in the form of a loop back again to the one end.

The circuit or measurement device thereof may be configured as a four-wire system in particular for voltage measurement, similar to the principle of a Thomson bridge (also known as a Kelvin bridge), with a reference resistor incorporated in the four-wire system, a difference amplifier and an analogue-digital converter, in order to enable precise detection of even relatively small resistance values of an indicator line. Such a further development for example provides the or each measurement loop with its own separate instrumentation amplifier, which is connected on the input side to both end points of the indicator conductors, and on the output side to an analogue-digital converter, in particular an analogue-digital converter integrated into the logic circuit. A reference resistor is preferably connected in series to the measurement loop(s), wherein a constant-current source feeds a measurement current through the measurement loop(s) and optionally the reference resistor. By means of the reference resistor, the voltage measurement may detect even a very small measurement loop resistance from the two indicator conductors sufficiently precisely using a four-wire system, similar to the principle of a Thomson bridge.

Preferably, the measurement loop formed by the two-part, outward and return indicator conductor is formed on the basis of two additional, dedicated or assigned measurement cores in an active multicore supply cable, the remaining cores of which serve the actual supply purpose, for example data transmission or power supply.

The dedicated measurement cores are preferably short-circuited using a short-circuit component at the moving end and are connected at the base end to the measurement device of the circuit, i.e. the circuit and optionally the evaluation unit may simply be arranged on the stationary part of the installation. The configuration of the wiring may optionally also be reversed if the circuit is provided at the moving end, which is appropriate in particular for an evaluation unit 5 arranged on the displaceable machine part.

To monitor the condition of a cable, it is particularly advantageous for the measurement cores, which form the substantial part of the indicator conductors, to be twisted together or optionally braided with other active cores in a supply cable used in operation for its intended purpose. This makes detection as meaningful and close to reality as possible with regard to the wear of the active cores which are actually to be monitored. In this case, the measurement cores may in particular be of like construction to at least one operationally active core and twisted or braided in a similar manner thereto. The measurement cores may in particular be of like construction to the core most prone to wear. In the case of lines of large cross-section, it is also conceivable to embody the measurement cores with smaller conductor cross-sections and interpolate the condition of a thicker main core, in particular by means of the evaluation unit.

The integrated logic circuit or, particularly preferably, the evaluation unit preferably has an operator input for inputting a resistance or conductance measured on start-up by the measurement device as reference value. This makes it simple even for the end users themselves to define the normal value for the original or wear-free condition of the measurement loop or the indicator conductors. In this way, the monitoring device is inherently programmed in an application-specific manner, without its being necessary to know for example the length of the energy guide chain or similar data.

It is advantageous, in particular in conjunction with the latter feature, for the evaluation unit to be programmed to trigger a warning signal when the resistance or conductance of the indicator conductor differs from the reference value by a predetermined amount, in particular an amount in the range from 15-25% of the reference value. Taking an empirically determined amount as threshold value, cable monitoring can be carried out if only the original normal value for resistance or conductance is known.

The following further developments are advantageous for all above aspects, i.e. also for position monitoring and/or line condition monitoring.

The evaluation unit preferably includes a memory for application data and comprises a logic circuit which evaluates the signal output by the circuit in dependence on stored application data. This construction for example allows nominal values or a tolerance field to be learned. Reference data may thus, for example, be recorded in an initialization process during normal movement, as intended, of a new energy guide chain with the circuit and stored in the evaluation unit. The application- and/or position-specific reference data may for example be obtained from a test laboratory and prestored in the evaluation unit or transmitted thereto.

In the latter case in particular, the evaluation unit may include an input via which the current position of the moving end is detected. This makes it possible to read out a currently valid position-dependent reference value from the memory, which is significant in particular for geometry-sensitive quantities.

The evaluation unit may comprise a communication interface, for example a WLAN interface, for connection to a higher-level system, for reading in or transmitting data, for example for initialization, for maintenance purposes or for data collection on the manufacturer's premises.

It is advantageous, in particular for precise instrumental detection, for the monitoring device to include a temperature sensor for temperature normalization. This may be provided, for example, as a component part of an evaluation unit of modular construction.

To increase modularity, the device may include as part of the circuit or of the evaluation unit a logic circuit, in particular a microcontroller, ASIC, DSP or the like, which digitally processes the detected electrical quantity, in particular for comparison with a reference value from a reference value memory. This is advantageous in particular if the circuit performs analogue detection of the electrical quantity 11.

In ongoing operation of the energy guide chain, the circuit may detect the electrical quantity continuously or in time-discrete manner at uniform or random intervals. In this respect, a filter, in particular an average or peak filter, is preferably provided in the circuit or the evaluation unit, in order to filter out irrelevant fluctuations owing for example to electromagnetic interference and the like.

The device may, in particular in the form of a module, be arranged stationarily on the base, wherein the indicator conductor is connected single-endedly to the circuit at the connection end for the base.

The basic principle of the monitoring system proposed here is suitable for ongoing operation, both for monitoring the spatial course of the energy guide chain in ongoing operation and for monitoring the condition of a data or power supply cable of an energy guide chain in continuous operation. The systems serve in particular in preventive maintenance and/or safety shutdown.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantageous features and effects of the invention are explained in greater detail below on the basis of a number of preferred exemplary embodiments and with reference to the appended drawings, in which:

FIGS. 1A-1B: show schematic diagrams in side view (FIG. 1A) and schematic cross-section (FIG. 1B) of a monitoring system;

FIGS. 2A-2B: show schematic diagrams in side view (FIG. 2A) and schematic cross-section (FIG. 2B) of a monitoring system according to one variant;

FIG. 3 : shows a diagram of a tolerance field within which an electrical quantity at the indicator conductor should lie;

FIG. 4 : shows a schematic diagram in side view of a third exemplary embodiment of a monitoring system;

FIG. 5 : shows a schematic diagram in side view of a fourth example of a monitoring system according to a further variant, with a wireless communication interface to a communication module;

FIGS. 6A-6B: show schematic diagrams in side view (FIG. 6A) of an exemplary embodiment according to the invention of a monitoring system according to a further aspect, with a wireless communication interface to a communication module, and as a separate circuit module (FIG. 6B) for monitoring the condition of a cable in an energy guide chain; and

FIG. 7 : shows a photo of a partly stripped electrical supply cable with twisted cores.

DETAILED DESCRIPTION

In all the drawings, identical reference numerals denote features of an equivalent nature or with an equivalent effect. Repetition is avoided for the purpose of simplification.

FIGS. 1-7 show an energy guide chain, denoted overall as 1, with a flat, stationary run 1A, also known as the lower run when arranged horizontally, a mobile run 1B, also known as the upper run when arranged horizontally, and with a displaceable, approximately U-shaped deflection arc 1C, as a movable transition therebetween, which ensures a predefined radius of curvature. A “sliding”, i.e. non-self-supporting energy guide chain 1 for long travel paths, typically of >3 m is shown here. With such energy guide chains 1, the mobile run 1B may slide or roll on the stationary run 1A. Per se known skids or casters are not shown. To protect the guided lines (not shown), the predefined radius of curvature of the deflection arc 1C is markedly greater than the contact spacing between the runs 1A, 1B. The invention is however in principle also suitable for self-supporting energy chains or vertical applications (not shown).

The end region of the stationary run 1A forms a first connection point for the energy guide chain 1 and is fastened to a base fixed relative to the surrounding environment, which forms the fixed point 2 of the energy guide chain 10. The end region of the mobile run 1B forms a second connection point for the energy guide chain 1 and is fastened at a moving end 4, which is mobile relative to the fixed point 2, namely to the moving part to be supplied, for example of an industrial machine or installation.

In a manner known per se, the moving end 4 moves in a forward and backward direction in accordance with the double-headed arrows in FIGS. 1-7 and in so doing respectively pulls and pushes the energy guide chain 1. In FIGS. 1-7 , the moving end 4 and thus the position of the energy guide chain 10 are shown purely by way of example, as illustrative snapshots or instantaneous intermediate positions. The energy guide chain 1 is configured for virtually planar movement in the forward and backward directions, i.e. with runs 1A, 1B which remain parallel, and consists substantially of chain links (not shown in greater detail) which can be bent relative to one another for example about parallel pivot axes pivotable perpendicular to the plane of FIGS. 1-7 . In all the embodiments, the energy guide chain 1 may be guided at the sides in a guide channel 5 shown schematically in greater detail in FIG. 1B.

A fault condition (indicated as a “lightning bolt”) involving a sub-region of the mobile run 1B climbing undesirably, which is unusual but possible particularly with long or fast-moving energy guide chains 1, is shown here purely schematically and exaggeratedly solely by FIG. 1A and FIG. 2A. FIG. 6A shows by way of example a normal course of the energy guide chain 1.

The exemplary embodiment according to FIGS. 1A-1B shows, as core elements of the sensor unit, a monitoring system 10 with an electrical indicator conductor 12 guided along the two runs 1A, 1B and around the deflection arc 1C of the energy guide chain 1. The single indicator conductor 12 is arranged as a dipole or doublet antenna and connected solely at the final node on the base 2 to a circuit 14. The circuit 14 comprises a signal generator which feeds a high frequency excitation signal, for example an alternating current sine signal with a frequency of a few Mhz into the indicator conductor 12. The circuit 14 additionally has an SWR meter (not shown), which detects the standing wave ratio (SWR) as an electrical quantity by means of the indicator conductor 12. The SWR is dependent on the spatial position of the indicator conductor 12 and thus of the energy guide chain 1, in particular of the mobile run 1B. Detection of the SWR makes it possible to identify a fault condition (indicated as a “lightning bolt”) by comparison with a setpoint SWR characteristic (cf. 30 in (FIG. 3 )) learned during start-up. Instead of the SWR meter, a network analyzer or a simpler circuit may for example also be suitable for measuring the reflected wave in the case of an unchanging excitation frequency. The circuit 14 is connected on the output side to an evaluation unit 6, which for example evaluates an output signal, indicating the SWR, of the circuit 14 and triggers an emergency stop in good time in the event of a fault condition.

In the variant according to FIGS. 2A-2B, the indicator conductor 22 forms a measurement loop or loop antenna and is arranged in the circuit 24 as an inductive part of an RLC oscillating circuit. The two end points of two measurement cores 22A, 22B at the base 2 are connected directly to the remaining components of the oscillating circuit of the circuit 24. The distal end points, for example at the moving end 4, are short-circuited by means of a low-resistance short-circuit component 23, as shown in FIG. 2B. Since induction is here also geometry-dependent, the circuit 24 can identify a change in the coil induction of the measurement loop as measured value 30 in comparison with a normal characteristic between two tolerance curves 31, 32, as indicated schematically in FIG. 3 . This may proceed by means of a microcontroller 25 as part of the circuit 24 or in the evaluation unit 6, for example by identifying an abnormal jump in the detected electrical quantity of the two-part indicator conductor 22.

FIG. 4 shows a variant of the monitoring system 40 consisting of two oscillating circuits for detecting an unexpected change in beat frequency by superimposition. The indicator conductor 42 here also forms a loop or coil of two measurement cores 42A, 42B, which are also guided from the base 2 to the moving end 4 in the energy guide chain and are bridged at the moving end by the short-circuit component 43.

The circuit forms a first measuring oscillating circuit 46, with a capacitor (C2) and the measurement loop 42 as inductor, to which a sine signal is applied by a signal generator 48. As a function of a measurement run or teaching on start-up, a reference oscillating circuit 47 simulates the normal behavior of the measuring oscillating circuit 46 when the energy guide chain 1 is running as intended, wherein the behavior thereof is dependent on the position of the moving end 4. Simulation may be achieved for example by an input measured value sequence or an adjustable oscillator in a microcontroller 45. By means of a mixer stage 49, a beat frequency is then generated on the basis of the oscillation detected at the measuring oscillating circuit 46 and the position-dependently simulated oscillation of the reference oscillating circuit 47. The beat frequency generated or simulated by the mixer stage 49 is then compared for example with a tolerance field 31, 32 dependent on the position X of the moving end 4, as shown schematically in FIG. 3 . This variant for example follows the principle of a metal detector, and may in particular be used with a guide channel 5 of ferromagnetic sheet steel or the like.

In a variant not shown in any greater detail, a separate excitation or transmit coil may also be provided together with the measurement loop consisting of the measurement cores 42A, 42B, for example according to the principles of other metal detector types.

FIG. 5 shows a further, inductively detecting monitoring system 50, wherein the guide channel 5 acts in a similar manner to a “ferrite core”. The loop-shaped indicator conductor 52 is excited by an oscillator 55 as signal generator and measured. A demodulator 56 leads the detected signal to a discriminator or hysteresis comparator 57, and onward to an output stage, which provides an output signal 51 for the evaluation unit 6. Learned normal values or tolerance curves 31, 32 may here be input into the evaluation unit 6 on start-up or via a data link such as for example WLAN with a communication module 7.

The above-described monitoring systems 10, 30, 40, 50 allow, in particular on the basis of electromagnetic interaction, the identification of a deviation in the position of the energy guide chain 1 from its nominal setpoint course.

A further, independent aspect is described below, namely a system 60 for wear monitoring of electrical conductors or cores in a supply cable of an active energy guide chain to provide early warning of an impending cable break.

The circuit module 64 has two status indicators for example (ACTIVE, ERROR: FIG. 6B) and a button (SET: FIG. 6B) for inputting a nominal resistance value into a memory register in a microcontroller 65 of the circuit module 64.

An instrumentation or difference amplifier (OpAmp) 66 is connected directly to the final nodes of two measurement cores 62A, 62B, which form a loop-shaped indicator conductor 62 in the energy guide chain 1, which is short-circuited at the moving end 4 via a component 23. The output of the instrumentation amplifier 66 is connected to the input of an A/D converter 67 in the microcontroller 65 converter, which taps a voltage of a reference resistor 69 at two further inputs. The series-connected measurement cores 62A, 62B are connected in series to the reference resistor 69 (Rref) and are supplied with a constant current by a reference direct current source 68 (constant-current source) of the circuit module 64 (I0). The inputs of the ADC 67 detect on the one hand the measurement voltage dropping across the measurement loop 62A, 62B in order to determine the relatively low ohmic series resistance Rx thereof by means of the current (I0) and on the other hand, according to the four-wire measurement principle, the voltage at the reference resistor 69 (Rref), from the ratio of which the resistance Rx to be measured is determined precisely with the microcontroller 65.

To increase detection reliability, a plurality of measurement loops 62A, 62B may also be measured in each case via their own difference amplifier 66 and corresponding input of the ADC 67. As an alternative to the resistance, a conductance may naturally also equally well be determined. The measuring line, i.e. in each case a proximal final node of the measurement cores 62A, 62B close to the base 2, is connected to terminals M1 and M2 (FIG. 6B) of the circuit module 64. The two distal final nodes of measurement cores 62A, 62B are short-circuited or connected together with low resistance. For normalization purposes, a temperature sensor 63 is connected to the circuit module 64 (terminals T2 and T3).

The microcontroller 65 causes the ACTIVE LED to light up green as soon as the circuit module 64 is connected (via the + and − terminals) to a voltage supply (for example 24 V DC) and the reference value is input. On start-up, the reference value is programmed into the microcontroller 65 on a one-off basis by actuating the SET button, by initial measurement via the instrumentation amplifier 66 as above.

The green and red ERROR LEDs light up as soon the resistance Rx of the line measured by the microcontroller 65 has exceeded a predetermined warning threshold value (for example 1.25×Rx). The warning threshold value may be empirically determined from life tests and optionally also subsequently changed or updated, for example via the communication module 7. Furthermore, the microcontroller 65 may close a warning signal contact (O1) via an output by a relay (not shown).

If a cable break has occurred (Rx tending towards infinity), the green LED goes out, for example, leaving only the red ERROR LED lit up. In addition, the microcontroller 65 then closes a further potential-free fault contact (O2).

The warning signal is preferably transmitted via a communication interface, for example an industrial bus, RS-232 or the like (3.3 V, TX, GND) to the here optional evaluation unit 6 or directly to an internet-capable communication module 7.

Via the communication interface (3.3 V, TX, GND) of the circuit module 64, the microcontroller 65 may transmit detected measurement data (resistance, constant current, voltage drop, temperature etc.) to the optional evaluation unit 6 or directly to the communication module 7. The circuit module 64 may alternatively or additionally include a data logger (for example a Micro SD card) for storing measured data. In addition, sensor inputs may be provided as a cycle counter or for position detection (for example according to FIGS. 1-5 ). When programming the microcontroller 65, a software filter may be provided for filtering out disruptive influences 5 caused for example by electromagnetic interaction with other active lines. The resistance of the measurement cores 62A, 62B may be measured periodically, for example with a spacing of a few minutes, or at quasi-random time intervals, to avoid artifacts caused for example by harmonics and the like.

FIG. 7 shows purely by way of example and for illustrative purposes how measurement cores 62A, 62B are twisted together with active supply cores in a supply cable 70, wherein the measurement cores 62A, 62B are of like construction to at least other operationally active supply cores.

LIST OF REFERENCE SIGNS

FIGS. 1-6

-   1 Energy guide chain -   1A Stationary run -   1B Mobile run -   1C Deflection arc -   2 Fixed point -   4 Moving end -   5 Guide channel -   6 Evaluation unit -   7 Communication module     FIGS. 1A-1B -   10 Monitoring system -   11 Signal -   12 Indicator conductor -   14 Circuit     FIGS. 2A-2B -   20 Monitoring system -   22 Indicator conductor -   22A, 22B Measurement cores -   23 Short-circuit component -   24 Circuit -   25 Microcontroller -   26 Oscillating circuit     FIG. 3     X Position of moving end     Y Amount (of the electrical quantity)     30 Measured value (of the electrical quantity)     31 Lower tolerance curve     32 Upper tolerance curve     FIG. 4 -   40 Monitoring system -   42 Indicator conductor -   42A, 42B Measurement cores -   43 Short-circuit component -   44 Circuit -   45 Microcontroller -   46 Measuring oscillating circuit -   47 Reference oscillating circuit (simulated) -   48 Signal generator -   49 Mixer stage     FIG. 5 -   50 Monitoring system -   51 Signal -   52 Indicator conductor -   54 Circuit -   55 Oscillator (signal generator) -   56 Demodulator -   57 Comparator -   59 Output stage     FIG. 6 -   60 Monitoring system -   61 Signal -   62 Indicator conductor (Rx) -   62A, 62B Measurement cores -   63 Temperature sensor -   64 Circuit module -   65 Microcontroller -   66 Difference amplifier -   67 A/D converter -   68 Current source -   69 Reference resistor (Rref)     FIG. 7 -   70 Electrical supply cable -   72 Active cores -   62A, 62B Measurement cores 

What is claimed:
 1. A monitoring system for monitoring condition of at least one line, comprising: an energy guide chain which is displaceable along a travel path and, in so doing, forms a mobile run with a connection end for a moving end, a stationary run with a connection end for a base and a deflection arc between the two runs, wherein the at least one line is guided in the energy guide chain between the base and the moving end movable relative thereto, and a monitoring device with at least one sensor unit arranged on the energy guide chain, which monitoring device evaluates a signal generated using the sensor unit in order to monitor occurrence of a fault condition during operation of the energy guide chain, wherein the sensor unit includes two electrical indicator conductors guided by the energy guide chain and extending at least along a greater part of a length of the mobile run, and wherein the monitoring device comprises a circuit with a measurement device for measuring resistance or conductance, and wherein one end point of each of the two indicator conductors is connected at one connection end of the energy guide chain to the measurement device and a respective other end point of each of the two indicator conductors are short-circuited, such that the conductors form a measurement loop, the resistance or conductance of which is measurable by the measurement device.
 2. The monitoring system according to claim 1, wherein the monitoring device comprises an evaluation unit which includes an integrated logic circuit and a reference value memory, wherein the logic circuit receives an output signal from the measurement device and uses the output signal for comparison with at least one prestored reference value from the reference value memory.
 3. The monitoring system according to claim 2, wherein the integrated logic circuit has an operator input for inputting a resistance or conductance measured on start-up by the measurement device as the at least one prestored reference value and/or triggers a warning signal when the resistance or conductance of the indicator conductor differs from the reference value by a predetermined amount.
 4. The monitoring system according to claim 3, wherein the predetermined amount is in a range from 15-25% of the at least one prestored reference value.
 5. The monitoring system according to claim 2, wherein an analogue-digital converter is integrated into the integrated logic circuit.
 6. The monitoring system according to claim 1, wherein the measurement loop is provided with an instrumentation amplifier, which is connected on an input side to both end points of the indicator conductors, and on an output side to an analogue-digital converter.
 7. The monitoring system according to claim 6, wherein the analogue-digital converter is integrated into an integrated logic circuit.
 8. The monitoring system according to claim 6, wherein a reference resistor is connected in series to the measurement loop and a constant-current source feeds a measurement current through the measurement loop and optionally the reference resistor.
 9. The monitoring system according to claim 1, wherein the indicator conductors are embodied as two additional measurement cores in a multicore supply cable with active supply cores.
 10. The monitoring system according to claim 9, wherein the measurement cores are twisted together or braided together with the active supply cores in the supply cable.
 11. The monitoring system according to claim 10, wherein the measurement cores are of like construction to at least one active supply core and are twisted or braided in a similar manner thereto.
 12. The monitoring system according to claim 9, wherein the measurement cores are short-circuited using a short-circuit component at the moving end connection end and at the base end are connected to the measurement device.
 13. The monitoring system according to claim 1, further comprising an evaluation unit which includes a memory for application data and comprises a logic unit which evaluates the signal output by the circuit in dependence on stored application data.
 14. The monitoring system according to claim 13, wherein the evaluation unit comprises a communication interface for connection to a higher-level system.
 15. The monitoring system according to claim 1, wherein the monitoring device includes a temperature sensor for temperature normalization.
 16. The monitoring system according to claim 1, wherein a logic circuit is provided which digitally processes a detected electrical quantity for comparison with a reference value from a reference value memory.
 17. The monitoring system according to claim 16, wherein the logic circuit comprises at least one of a microcontroller, an ASIC or a DSP.
 18. The monitoring system according to claim 1, wherein, in ongoing operation of the energy guide chain, the circuit detects an electrical quantity continuously or in time-discrete manner.
 19. The monitoring system according to claim 18, wherein the filter is an average or peak filter.
 20. The monitoring system according to claim 1, wherein the monitoring device is arranged as a module stationarily on the base and at least one of the indicator conductors is connected single-endedly to the circuit at the connection end for the base.
 21. The monitoring system according to claim 1, wherein the monitoring system is configured to monitor a condition of a data or power supply cable of an energy guide chain. 